This invention pertains to apparatus for improving safety in the administration and management of intravenous regional anesthesia (IVRA) for both upper and lower limbs. IVRA is an alternative to general anesthesia for limb surgery. IVRA has proven to be a simple and useful technique for satisfactorily anesthetizing the upper limb and is potentially well suited for greatly expanded utilization in surgery of lower limbs and in outpatient settings. In these settings, which are rapidly increasing in number worldwide, there is a large and unmet need for a rapid, simple, safe and reliable technique for establishing limb anesthesia. However, significant practical problems with the technology of IVRA in the prior art have limited the acceptance of this promising technique.
IVRA is an anesthetic technique which requires the use of a pneumatic surgical tourniquet system. Surgical tourniquet systems of the prior art typically include an inflatable cuff for encircling a limb and an automatic pressure regulator for maintaining a pressure applied by the cuff to the limb near a reference pressure selected by an operator or determined automatically. Surgical tourniquet systems are frequently used on the upper and lower limbs to help maintain a bloodless operative field by regulating the maximum pressure applied to the limb by an encircling cuff at a pressure sufficient to stop arterial blood flow past the cuff for the duration of a surgical procedure. A "physiologic tourniquet" system is generally considered to be one which has the capability of maintaining the pressure applied by the cuff to the limb near the minimum pressure required to stop the flow of arterial blood past the cuff during the surgical procedure.
During surgical procedures performed under IVRA, the surgical tourniquet system serves an additional role of preventing liquid anesthetic agent introduced into the veins in the limb distal to the cuff from flowing proximally past the cuff and out of the limb into the circulatory system. For surgical procedures where IVRA is to be employed, special cuffs having dual bladders are often used for encircling the limb, resulting in a first bladder encircling the limb above a second bladder which also encircles the same limb distal to the first bladder. Alternatively, two separate single-bladder cuffs can be applied to the same limb. To maintain the pressures applied by one dual-bladder cuff or two single-bladder cuffs near selected reference pressures, one tourniquet instrument having a dual-channel automatic pressure regulator may be employed, or two separate tourniquet instruments, each having one automatic pressure regulator, may be employed. Regardless of whether one dual-bladder cuff or two separate cuffs are used, and regardless of whether one dual-channel tourniquet instrument or two single-channel tourniquet instruments are used, surgical procedures involving IVRA are typically conducted as follows.
IVRA is typically administered as follows. A dual-bladder cuff is first applied to the limb on which surgery is to be performed, so that the first and second inflatable bladders of the cuff encircle the same limb, with the first cuff bladder being located proximal to the second, and so that both cuff bladders are located between the heart and the operative site on the limb. The portion of the limb distal to both bladders is then exsanguinated, often by wrapping the limb with an elastic bandage, beginning at the end of the limb and wrapping tightly towards the heart up to the cuff location. While the limb is thus exsanguinated, the tourniquet instrument is typically used to inflate the first (proximal) cuff and maintain it at a first predetermined cuff pressure sufficient to stop the inflow of arterial blood past the first cuff bladder. The elastic bandage is removed and a liquid anesthetic agent such as lidocaine mixed with sterile saline is introduced into a vein in the limb through an intravenous cannula. After a sufficient period of time has elapsed to allow tissue distal to the first cuff bladder to be anesthetised by the agent, the second pneumatic channel of the tourniquet instrument (or a second tourniquet instrument) is used to inflate the second (distal) cuff bladder and maintain it near a second predetermined pressure sufficient to stop the inflow of arterial blood past the second cuff bladder. The first (proximal) cuff bladder is then de-pressurized. In this manner, only the second cuff bladder remains inflated, it applies pressure primarily to anesthetised limb tissue encircled by the second bladder to reduce cuff-related pain, and the portion of the limb distal to the second cuff bladder remains anesthetised. The anesthetic liquid is maintained in the veins in the limb distal to the second cuff bladder as long as the second cuff bladder remains pressurized to a sufficient pressure, thus maintaining the regional anesthesia in the limb distal to the second cuff bladder.
Occasionally during a surgical procedure involving the use of IVRA, an operator may intentionally change the pressures applied by one or both of the cuff bladders to the limb, and may intentionally de-pressurize one or both bladders of a dual-bladder cuff. This is most common during long surgical procedures involving the use of IVRA. For example, because the probability of injury to nerves in the limb encircled by a pressurizing cuff bladder is known to increase with increased pressure applied by the cuff bladder to the limb, the operator may change the pressure applied by one or both of the cuff bladders to be a pressure near to the minimum pressure estimated to be required to stop the inflow of arterial blood past the cuff bladder.
Also, during a surgical procedure involving IVRA, the operator may re-pressurize the first (proximal) cuff bladder to a predetermined pressure and de-pressurize the second (distal) cuff bladder to a level near atmospheric pressure, in order to reduce cuff pain by moving the location of pressure applied to the limb and by allowing liquid anesthetic agent to re-infiltrate tissue beneath the location of the second (distal) cuff bladder. In long surgical procedures involving IVRA, this may be followed by re-pressurization of the first (proximal) cuff bladder to a predetermined level sufficient to stop blood flow and leakage of liquid anesthetic agent, and by de-pressurization of the second (distal) bladder to a pressure near atmospheric pressure. In certain other instances, the operator may intentionally pressurize both cuff bladders simultaneously to a predetermined reference pressure, for example, in order to distribute the applied pressure over a larger area in an effort to reduce cuff-related pain. In still other instances, the operator may intentionally reduce the pressure of both cuff bladders to a near-atmospheric level for a period of time, for example to allow blood to flow briefly before closing the surgical site in order to locate bleeding vessels which require suturing or to temporarily perfuse tissue distal to the cuff.
A potentially serious hazard of IVRA is that the operator may make an error in attempting to change the pressures applied by one or both of the cuff bladders to the limb, or may make an error in attempting to de-pressurize one or both bladders the dual-bladder cuff. A serious error is one that causes both cuff bladders to be inadvertently deflated or depressurized simultaneously. Premature release of the liquid anesthetic agent soon after its introduction, as a result of the inadvertent deflation or depressurization of a cuff bladder so that both cuff bladders are at a pressure below the minimum pressure required to stop the inflow of arterial blood or the outflow of anesthetic liquid from the limb distal to both cuff bladders, is a serious and recognized hazard of prior art devices used for IVRA which may result in the anesthetic agent entering the circulatory system in a sufficiently high concentration to cause adverse reactions, including a range of minor adverse reactions and such serious adverse reactions as cardiovascular collapse, respiratory depression, epileptic-like seizures or even death. Also, inadvertent deflation or depressurization of a cuff bladder So that both cuff bladders are at pressures below the minimum pressure required to stop the inflow of arterial blood or the outflow of anesthetic liquid from the limb distal to the cuff, at any time after introduction of the liquid anesthetic agent, is hazardous in that it will result in the reduction or elimination of the regional anesthesia in the limb distal to the cuff.
The applicant is unaware of any surgical tourniquet system in the prior art which includes apparatus for detecting a potentially hazardous attempt to change cuff pressure in a procedure involving the use of IVRA that may result in the release of liquid anesthetic agent from the limb into systemic circulation. Further, the applicant in unaware of any surgical tourniquet system in the prior art which, having detected such a potentially hazardous condition, will alert the operator to the hazardous condition and will require a separate and discrete confirmation action by the operator before changing the cuff reference pressure to the potentially hazardous level.